Oregon Mouse,

I've had this occur several times within the last year and have talked with Sawyer about it. They recommended backflushing it under a hot water faucet and/or soaking it in vinegar then backflushing it. This has worked for me. Takes about a half hour of fiddling to restore full flow.

More recently I've been using the technique shown in the link below:


For me the problem might have been associated with using bleach (per instructions on water bags) to disinfect the filter. Have you used bleach at all?